Capture and detection of target nucleic acid in dipstick assays

ABSTRACT

Use of helper probes in dipstick assays is described. In a dipstick assay to test for the presence of a target nucleic acid in a sample solution, the sample solution is connected with the contact end of the dipstick to cause the sample solution is contacted with the contact end of the dipstick to cause the sample solution to move by capillary action to a capture zone of the dipstick at which target nucleic acid is captured. The target nucleic acid may be captured at the capture zone by a capture probe capable of hybridising to the target nucleic acid. A labelled detection probe capable of hybridising to the target nucleic acid may be used to detect the target nucleic acid at the capture zone. A helper probe may be used to enhance the binding of the capture and/or detection probe to the target nucleic acid, thereby improving the sensitivity of target nucleic acid detection. Dipsticks and kits are also described.

The present invention relates to methods for improved detection ofnucleic acid by dipsticks. Methods of the invention are used to test forthe presence of a target nucleic acid in a sample solution, for exampleto identify whether a patient is infected with a disease causingmicroorganism such as Chlamydia trachomatis (CT).

Some conventional methods for testing for the presence of a targetnucleic acid in a sample solution rely on amplification of the targetnucleic acid using the polymerase chain reaction (PCR). Whilst thisreaction allows detection of small quantities of target nucleic acid, itcan is take several hours before a result is obtained. This can be asignificant disadvantage because it is often desired to obtain theresult as soon as possible, for example, to keep patient waiting timesto a minimum. Further disadvantages of such methods are the requirementfor expensive specialist equipment to perform the reaction and therelatively high cost of the reagents.

In contrast, dipsticks can detect unamplified target nucleic acidwithout the requirement for any specialist equipment. The results can beobtained much more rapidly than PCR-based methods and, therefore, in asingle visit from a patient. The patient can then be treated in the samevisit. This is particularly advantageous where the patient is unlikelyto, or cannot return for treatment at a later date. The cost ofperforming a dipstick test can also be significantly lower than the costof a PCR-based test.

In a typical, conventional dipstick described in U.S. Pat. No.5,310,650, a single stranded DNA capture probe is immobilised on anitrocellulose filter at a capture zone remote from one end of thefilter (the contact end). The sequence of the capture probe iscomplementary to the sequence of a first region of the target nucleicacid to be detected. A labelled single stranded DNA detection probe isreleasably immobilised on the nitrocellulose filter at a probe zonelocated between the capture zone and the contact end of the filter. Thesequence of the detection probe is complementary to the sequence of asecond region (distinct from the first region) of the target nucleicacid.

To detect target DNA in a sample solution thought to contain target DNA,the contact end of the nitrocellulose filter is contacted with thesample solution. The sample solution wicks up the filter by capillaryaction and passes the probe zone and the capture zone. As the samplesolution passes the probe zone, it mobilises the detection probe andcauses it to rise with the sample solution towards the capture zone.Mobilised detection probe can then hybridise to the second region of anytarget DNA present in the sample solution. When the hybridised detectionprobe and target DNA arrive at the capture zone, the first region of thetarget DNA can hybridise to the immobilised capture probe. A ternarycomplex is thereby formed between the target nucleic acid, the captureprobe and the labelled detection probe. Presence of label at the capturezone, therefore, indicates that target DNA is present in the samplesolution.

With a second type of conventional dipstick, the labelled DNA detectionprobe is not immobilised on the nitrocellulose filter. Instead thedetection probe is added to the sample solution under conditionsallowing hybridisation of the detection probe to any target nucleic acidin the sample solution. The contact end of the nitrocellulose filter isthen contacted with the sample solution and as the sample solution wicksup the dipstick, target nucleic acid which is hybridised to thedetection probe rises up the nitrocellulose filter and may be capturedat the capture zone by the capture probe.

Although results can be obtained more rapidly using conventionaldipsticks than detection methods which require amplification of thetarget nucleic acid, the sensitivity of nucleic acid detection byconventional dipsticks can be low. The sensitivity of detection ofdouble stranded target nucleic acid by conventional dipsticks can beparticularly low especially as the size of the target nucleic acidincreases, and circular double stranded target nucleic acid is thoughtto be virtually undetectable using conventional dipsticks. Consequently,the presence of target nucleic acid in a sample solution can sometimesbe undetected. It is desired, therefore, to improve the sensitivity oftarget nucleic acid detection, in particular the sensitivity of doublestranded and circular double stranded target nucleic acid detection bydipsticks.

In its broadest sense, the invention provides use of a helper probe in adipstick assay to enhance the hybridisation of a capture and/ordetection probe to the target nucleic acid.

The term “dipstick assay” as used herein means any assay using adipstick in which sample solution is contacted with the dipstick tocause sample solution to move by capillary action to a capture zone ofthe dipstick thereby allowing target nucleic acid in the sample solutionto be captured and detected at the capture zone.

According to a first aspect of the invention there is provided a methodfor testing for the presence of target nucleic acid in a sample solutionwhich comprises:

a) providing a chromatographic strip having: a contact end forcontacting the sample solution; and a capture probe immobilised at acapture zone of the chromatographic strip remote from the contact end,the capture probe being capable of hybridising to a first sequence ofthe target nucleic acid;

b) incubating the sample solution with a detection probe capable ofattaching to the target nucleic acid under conditions for attachment ofthe detection probe to target nucleic acid, thereby allowing direct orindirect detection of target nucleic acid utilising the detection probe;and first helper probe capable of hybridising to a second sequence ofthe target nucleic acid and thereby enhancing hybridisation of thecapture probe to target nucleic acid, the sample solution and the firsthelper probe being incubated under conditions for hybridisation of thefirst helper probe to target nucleic acid;

c) contacting the contact end of the chromatographic strip with thesample solution so that a complex formed between the detection probe,the first helper probe and target nucleic acid can move by capillaryaction to the capture zone and bind to the capture zone by hybridisationof the capture probe to target nucleic acid of the complex; and

d) checking for the presence of detection probe at the capture zone.

There is also provided according to the first aspect of the invention akit for testing for the presence of target nucleic acid in a samplesolution suspected of containing target nucleic acid which comprises:

i) a dipstick comprising:

a chromatographic strip having a contact end for contacting the samplesolution; and

a capture probe immobilised at a capture zone of the chromatographicstrip remote from the contact end, the capture probe being capable ofhybridising to a first sequence of the target nucleic acid;

ii) a first helper probe capable of hybridising to a second sequence ofthe target nucleic acid and thereby enhancing hybridisation of thecapture probe to the target nucleic acid; and optionally

iii) a detection probe capable of attaching to target nucleic acid toallow direct or indirect detection of the target nucleic acid utilisingthe detection probe.

The term “chromatographic strip” used herein means any porous strip ofmaterial capable of transporting a solution by capillarity.

The detection probe and the first helper probe may be incubated with thesample solution in any order or they may be added at the same time tothe sample solution.

It will be understood that the contact end of the chromatographic stripwill normally be contacted with the sample solution after the samplesolution has been incubated with the detection probe and the firsthelper probe according to step (b). However, it is not essential for theworking of the invention that the contact end is contacted with thesample solution after step (b) has been completed—the contact end of thechromatographic strip may be contacted with the sample solution beforeor during step (b).

The capture probe of the first aspect of the invention may comprise asingle probe, or more than one probe. For example the capture probe maycomprise a universal capture probe immobilised to the chromatographicstrip and a hook capture probe hybridised to the universal captureprobe, the hook probe being capable of hybridising to the first sequenceof the target nucleic acid.

An advantage of using a universal probe and a hook probe as the captureprobe is that chromatographic strips which have the universal probeimmobilised to them may be used to detect any target nucleic acid. Ahook probe capable of hybridising to the desired target nucleic acid issimply selected and hybridised to the universal probe before thechromatographic strip is used to test for the presence of the desiredtarget nucleic acid.

According to a second aspect of the invention there is provided a methodfor testing for the presence of target nucleic acid in a sample solutionwhich comprises:

a) providing a chromatographic strip having: a contact end forcontacting the sample solution; and a capture moiety immobilised at acapture zone of the chromatographic strip remote from the contact end;

b) incubating the sample solution with: a detection probe capable ofattaching to the target nucleic acid under conditions for attachment ofthe detection probe to target nucleic acid, thereby allowing direct orindirect detection of target nucleic acid utilising the detection probe;

a capture probe capable of hybridising to a first sequence of the targetnucleic acid under conditions for hybridisation of the capture probe tothe first sequence, the capture probe being capable of being bound bythe capture moiety when the capture probe has hybridised to the firstsequence; and

a first helper probe capable of hybridising to a second sequence of thetarget nucleic acid and thereby enhancing hybridisation of the captureprobe to target nucleic acid, the sample solution and the first helperprobe being incubated under conditions for hybridisation of the firsthelper probe to the second sequence;

c) contacting the contact end of the chromatographic strip with thesample solution so that a complex formed between the detection probe,the capture probe, the first helper probe and target nucleic acid canmove by capillary action to the capture zone and bind to the capturezone by binding of the capture moiety to the capture probe of thecomplex; and

d) checking for the presence of detection probe at the capture zone.

According to the second aspect of the invention there is also provided akit for testing for the presence of a target nucleic acid in a samplesolution which comprises:

i) a dipstick comprising:

a chromatographic strip having a contact end for contacting the samplesolution; and a capture moiety immobilised at a capture zone of thechromatographic strip remote from the contact end;

ii) a capture probe capable of hybridising to a first sequence of thetarget nucleic acid and which can be bound by the capture moiety whenthe capture probe has hybridised to the first sequence;

iii) a first helper probe capable of hybridising to a second sequence ofthe target nucleic acid and thereby enhancing hybridisation of thecapture probe to the first sequence; and optionally

iii) a detection probe capable of attaching to the target nucleic acidto allow direct or indirect detection of the target nucleic acid.

The capture moiety of the second aspect of the invention may comprise auniversal capture probe capable of hybridising to the capture probe.Alternatively the capture moiety may be capable of binding by non basepairing interaction to the capture probe once the capture probe hashybridised to the target nucleic acid.

For example, the capture moiety may comprise an antibody or antibodyfragment capable of binding to the duplex formed when the capture probehas hybridised to the target nucleic acid. Alternatively, the captureprobe may comprise a capture ligand which can be bound by the capturemoiety. When the capture probe comprises a capture ligand the capturemoiety may comprise an antibody or antibody fragment. If the captureligand comprises biotin the capture moiety may comprise an anti-biotinantibody or streptavidin, avidin, or a derivative thereof which retainsbiotin binding activity.

The second sequence of the first and second aspects of the inventionshould be in a different region of the target nucleic acid to the firstsequence. Preferably the second sequence is spaced up to 10 nucleotidesfrom the first sequence. More preferably the second sequence isimmediately adjacent the first sequence.

In preferred methods of the first and second aspects of the inventionthe sample solution is incubated with a second helper probe capable ofhybridising to a third sequence of the target nucleic acid and therebyenhancing hybridisation of the capture probe to target nucleic acid, thesample solution and the second helper probe being incubated underconditions for hybridisation of the second helper probe to targetnucleic acid.

The third sequence should be in a different region of the target nucleicacid to the first and second sequences. Preferably the second and thirdsequences flank the first sequence. More preferably the second and thirdsequences are spaced up to 10 nucleotides each side of the firstsequence. Most preferably the second and the third sequence areimmediately adjacent each side of the first sequence.

The capture probe, detection probe and helper probes may comprisenucleic acids or nucleic acid analogues. The capture probe may comprisea single probe, or more than one probe.

The detection probe of the first and second aspects of the invention maybe a label which covalently attaches to the target nucleic acid therebyallowing direct detection of target nucleic acid. Alternatively thedetection probe may be a ligand which covalently attaches to the targetnucleic acid thereby allowing indirect detection of target nucleic acidusing a ligand binding moiety capable of binding to the ligand. Thedetection probe may be added to the sample solution in the form of aprecursor which reacts with the target nucleic acid to covalently attachthe detection probe to the target nucleic acid.

Alternatively, the detection probe may be capable of attaching to thetarget nucleic acid by non covalent interaction. For example, thedetection probe may be capable of hybridising to a fourth sequence ofthe target nucleic acid. The detection probe may be labelled therebyallowing direct detection of the target nucleic acid when the detectionprobe has attached to the target nucleic acid by non covalentinteraction. Alternatively, the detection probe may comprise a ligandthereby allowing indirect detection of the target nucleic acid using aligand binding moiety when the detection probe has attached to thetarget nucleic acid by non covalent interaction.

Preferred labels are non radioactive labels. Examples of suitable labelsinclude textile dyes, metal sol such as colloidal gold and colouredparticles such as coloured latex particles. Examples of suitable ligandsinclude biotin (detectable for example by an anti-biotin antibody, or bystreptavidin or avidin or a derivative thereof which retains biotinbinding activity), fluorescein (detectable for example by ananti-fluorescein antibody), and 2,4-dinitrophenol (DNP) (detectable forexample by an anti-DNP antibody).

Further improved sensitivity of detection of target nucleic acid may beobtained if the sample solution is incubated with a third and,preferably, also with a fourth helper probe. The third helper probe iscapable of hybridising to a fifth sequence of the target nucleic acidand the fourth helper probe is capable of hybridising to a sixthsequence of the target nucleic acid, thereby enhancing hybridisation ofthe detection probe to the fourth sequence. The sample solution and thethird and fourth helper probes are incubated under conditions forhybridisation of the third and fourth helper probes to target nucleicacid.

It is possible that any significant enhancement of the sensitivity ofdetection using the third and fourth helper probes may only be observedwhen the first and the fourth sequences of the target nucleic acid areat least 200 nucleotides apart.

Preferably the fifth and sixth sequences flank the fourth sequence. Morepreferably the fifth and sixth sequences are spaced up to lo nucleotideseach side of the fourth sequence. Most preferably the fifth and sixthsequences are immediately adjacent each side of the fourth sequence.

According to a third aspect of the invention there is provided a methodfor testing for the presence of target nucleic acid in a sample solutionwhich comprises:

a) providing a chromatographic strip having: a contact end forcontacting the sample solution; and a capture probe immobilised at acapture zone of the chromatographic strip remote from the contact end,the capture probe being capable of hybridising to a first sequence ofthe target nucleic acid;

b) incubating the sample solution with:

a detection probe capable of hybridising to a second hybridisation ofthe detection probe to target nucleic acid, thereby allowing direct orindirect detection of target nucleic acid utilising the detection probe;and

a first helper probe capable of hybridising to a third sequence of thetarget nucleic acid and thereby enhancing hybridisation of the detectionprobe to the second sequence, the sample solution and the first helperprobe being incubated under conditions for hybridisation of the firsthelper probe to the third sequence;

c) contacting the contact end of the chromatographic strip with thesample solution so that a complex formed between the detection probe,the first helper probe and target nucleic acid can move by capillaryaction to the capture zone and bind to the capture zone by hybridisationof the capture probe to the target nucleic acid of the complex; and

d) checking for the presence of detection probe at the capture zone.

According to the third aspect of the invention there is also provided akit for testing for the presence of a target nucleic acid in a samplesolution suspected of containing target nucleic acid which comprises:

i) a dipstick comprising:

a chromatographic strip having a contact end for contacting the samplesolution; and a capture probe immobilised at a capture zone of thechromatographic strip remote from the contact end, the capture probebeing capable of hybridising to a first sequence of the target nucleicacid;

ii) a detection probe capable of hybridising to a second sequence of thetarget nucleic acid to allow direct or indirect detection of the targetnucleic acid; and

iii) a first helper probe capable of hybridising to a third sequence ofthe target nucleic acid and thereby enhancing hybridisation of thedetection probe to the second sequence.

The capture probe of the third aspect of the invention may comprise asingle probe, or more than one probe. For example the capture probe maycomprise a universal capture probe immobilised to the chromatographicstrip and a hook capture probe hybridised to the universal captureprobe, the hook probe being capable of hybridising to the first sequenceof the target nucleic acid.

According to a fourth aspect of the invention there is provided a methodfor testing for the presence of target nucleic acid in a sample solutionwhich comprises:

a) providing a chromatographic strip having: a contact end is forcontacting the sample solution; and a capture moiety immobilised at acapture zone of the chromatographic strip remote from the contact end;

b) incubating the sample solution with:

a capture probe capable of hybridising to a first sequence of the targetnucleic acid under conditions for hybridisation of the capture probe tothe first sequence, the capture probe being capable of being bound bythe capture moiety when the capture probe has hybridised to the firstsequence;

a detection probe capable of hybridising to a second sequence of thetarget nucleic acid under conditions for hybridisation of the detectionprobe to the second sequence, thereby allowing direct or indirectdetection of target nucleic acid utilising the detection probe; and

a first helper probe capable of hybridising to a third sequence of thetarget nucleic acid and thereby enhancing hybridisation of the detectionprobe to target nucleic acid, the sample solution and the first helperprobe being incubated under conditions for hybridisation of the firsthelper probe to the third sequence;

c) contacting the contact end of the chromatographic strip with thesample solution so that a complex formed between the detection probe,the capture probe, the first helper probe and target nucleic acid canmove by capillary action to the capture zone and bind to the capturezone by binding of the capture moiety to the capture probe of thecomplex; and

d) checking for the presence of detection probe at the capture zone.

According to the fourth aspect of the invention there is also provided akit for testing for the presence of a target nucleic acid in a samplesolution suspected of containing target nucleic acid which comprises:

i) a dipstick comprising:

a chromatographic strip having a contact end for contacting the samplesolution; and a capture moiety immobilised at a capture zone of thechromatographic strip remote from the contact end;

ii) a capture probe capable of hybridising to a first sequence of thetarget nucleic acid and which can be bound by the capture moiety whenthe capture probe has hybridised to the first sequence;

iii) a detection probe capable of hybridising to a second sequence ofthe target nucleic acid to allow direct or indirect detection of thetarget nucleic acid; and

iv) a first helper probe capable of hybridising to a third sequence ofthe target nucleic acid and thereby enhancing hybridisation of thedetection probe to the second sequence.

The capture moiety of the fourth aspect of the invention may comprise auniversal capture probe capable of hybridising to the capture probe.Alternatively the capture moiety may be capable of binding by non basepairing interaction to the capture probe once the capture probe hashybridised to the target nucleic acid.

For example, the capture moiety may comprise an antibody or antibodyfragment capable of binding to the duplex formed when the capture probehas hybridised to the target nucleic acid. Alternatively, the captureprobe may comprise a capture ligand which can be bound by the capturemoiety. When the capture probe comprises a capture ligand the capturemoiety may comprise an antibody or antibody fragment. If the captureligand comprises biotin the capture moiety may comprise an anti-biotinantibody or streptavidin, avidin, or a derivative thereof which retainsbiotin binding activity.

The detection probe of the third and fourth aspects of the invention maybe labelled thereby allowing direct detection of the target nucleic acidwhen the detection probe has hybridised to the target nucleic acid.Alternatively, the detection probe may comprise a ligand therebyallowing indirect detection of the target nucleic acid using a ligandbinding moiety when the detection probe has hybridised to the targetnucleic acid.

The third sequence in methods of the third and fourth aspect of theinvention is preferably spaced up to 10 nucleotides from the secondsequence. More preferably the third sequence is immediately adjacent thesecond sequence.

Preferably in methods of the third and fourth aspects of the inventionthe sample solution is incubated with a second helper probe capable ofhybridising to a fourth sequence of the target nucleic acid and therebyenhancing hybridisation of the detection probe to target nucleic acid,the sample solution and the second helper probe being incubated underconditions for hybridisation of the second helper probe to the fourthsequence.

Preferably with methods of the third and fourth aspects of the inventionthe third and fourth sequences flank the second sequence. Morepreferably the fourth sequence is spaced up to 10 nucleotides from thesecond sequence. Most preferably the fourth sequence is immediatelyadjacent the second sequence.

It is possible that any significant enhancement of the sensitivity ofdetection using the first and second helper probes in methods of thethird and fourth aspects of the invention may only be observed when thefirst and the second sequences of the target nucleic acid are at least200 nucleotides apart.

If the detection probe of a kit of the invention comprises a detectionligand, the kit may further comprise a labelled detection ligand bindingmoiety capable of binding to the detection ligand thereby enablingdetection of target nucleic acid utilising the detection probe and thedetection ligand binding moiety. The detection ligand binding moiety maybe an antibody, an antibody fragment or a non antibody.

Kits of the invention may further comprise any reagent required to allowdetection of target nucleic acid in the sample solution utilising thechromatographic strip.

There is also provided according to the invention a substantiallyisolated nucleic acid molecule or nucleic acid analogue having asequence corresponding to the sequence of any of SEQ ID NOS: 1-18.

There is also provided according to the invention use of a substantiallyisolated nucleic acid molecule or nucleic acid analogue of the inventionas a helper probe to enhance detection of CT target nucleic acid in atest for the presence of such target nucleic acid in a sample solution.

The helper probes used in methods of the invention may enhance thebinding of capture or detection probes to single stranded or doublestranded target nucleic acid. Where the target nucleic acid is singlestranded, it is thought that the helper probe may enhance the binding ofthe capture/detection probe to the target nucleic acid by ensuring thatthe target nucleic acid does not form significant secondary structure inthe region of the target nucleic acid to which the capture/detectionprobe binds.

It will be appreciated that the region of the target nucleic acid towhich the helper probe binds may not always be close to or immediatelyadjacent the region to which the capture/detection probe binds.Hybridisation of a helper probe to one region of target nucleic acidcould alter its secondary structure at a remote location, therebyallowing a capture/detection probe to bind more easily to the targetnucleic acid at that remote location.

Consequently, the region of the target nucleic acid to which the helperprobe binds is likely to differ depending on the identity of the targetnucleic acid and of the capture/detection probe. However, a personskilled in the art can readily determine which helper probes are mosteffective by experimenting with different probes and different lengthsof probe.

Where the target nucleic acid is double stranded, it is thought thathybridisation of a helper probe to the target nucleic acid enhanceshybridisation of the capture or detection probe to the target nucleicacid by opening up the double strands of the target nucleic acid in theregion in which the capture or detection probe binds. Consequently, fordouble stranded target nucleic acid, it will normally be expected that ahelper probe binds adjacent the region to which the capture or detectionprobe binds.

In order for a helper probe to enhance the binding of a capture ordetection probe to the target nucleic acid, the helper probe should behybridised to the target nucleic acid before or at the same time as thecapture or detection probe is hybiridised to the target nucleic acid,but not after the capture or detection probe has been hybridised to thetarget nucleic acid.

In some embodiments, a helper probe may enhance the hybridisation of acapture and a detection probe to the target nucleic acid. This may beachieved, for example, if the helper probe hybridises to a region of thetarget nucleic acid between the capture and detection probes.

In other embodiments of the invention, one or more of the probes may bereleasably immobilised to the chromatographic strip, between the contactend and the capture zone, in such a way that movement of the samplesolution from the contact end to the capture zone by capillary actionwill cause the or each probe to be released from the chromatographicstrip into the sample solution. Released probe can then hybridise totarget nucleic acid in the sample solution.

For embodiments of the invention in which a helper probe is providedwhich is capable of enhancing hybridisation of a detection probe to thetarget nucleic acid, the helper probe (preferably with the detectionprobe) may be contacted with the capture zone of the chromatographicstrip after the sample solution has been contacted with the contact endof the chromatographic strip to allow capture of target nucleic acid atthe capture zone. This may be achieved by applying a separate helperprobe solution containing the helper probe (and detection probe)directly to the capture zone, or by contacting the contact end of thechromatographic strip with the helper probe solution after the samplesolution, thereby causing the helper probe to move by capillary actionto the capture zone. If the detection probe is not in the helper probesolution, this will need to be contacted with the capture zone after thehelper probe.

However, in preferred methods of the invention, hybridisation of theprobes to target nucleic acid (other than where a capture probe isimmobilised at the capture zone) is carried out in the sample solutionbefore the sample solution is contacted with the chromatographic strip.Most preferably hybridisation of the probes is carried out in a singlestep. This simplifies the methods, thereby making them considerablyquicker and easier to perform.

Multiple step hybridisation may be carried out by sequentialhybridisation of the different probes to the target nucleic acid in thesample solution, or by contacting the dipstick with different solutionseach containing a different probe. Usually, the latter method ofmultiple step hybridisation will involve washing the dipstick betweeneach contact with a different probe solution.

Whilst there may be circumstances in which multiple step hybridisationis preferred, it will be appreciated that the simpler and quicker formatof one step hybridisation will usually be preferred.

It is most preferred that the sample solution is of suitable iscomposition to allow the hybridisation reactions to take place in asingle hybridisation step and also to allow non base pairinginteractions to take place (for example between a detection ligand and adetection ligand binding moiety and between a capture ligand and acapture ligand binding moiety) and transport a complex comprising targetnucleic acid and one or more hybridised probes and (optionally) ligandbinding moieties by capillary action up the dipstick.

Using such a sample solution, it will be appreciated that thehybridisation reactions can then be carried out in a single step, andany ligand-ligand binding moiety interactions can take place, before thesample solution is contacted directly with the contact end of thedipstick (without the need to first dilute or alter the samplesolution). Ligand-ligand binding moiety interactions can additionally oralternatively take place on the dipstick if desired as the samplesolution travels to the capture zone. Simple and rapid dipstickdetection of target nucleic acid is thereby facilitated.

We have found that such results are achieved with sample solutionscomprising a standard hybridisation buffer (such as SSPE buffer or Trisbuffer) with salt, detergent and a blocking protein such as BSA orpowdered milk. The sensitivity of detection of target nucleic acid usingsuch assays has been found to be about equal to or better than that ofother dipstick assays.

Embodiments of the invention are now described by way of example withreference to the accompanying drawings in which:

FIG. 1 shows a dipstick used to detect target nucleic acid in accordancewith an embodiment of the invention;

FIG. 2 lists the sequences of helper probes which can be used inaccordance with the invention;

FIG. 3 shows the experimental setup for Example 1;

FIG. 4 shows the experimental setup for Example 2;

FIG. 5 shows the experimental setup for Example 3;

FIG. 6 shows the experimental setup for Example 4;

FIG. 7 shows the experimental setup for Example 5;

FIG. 8 shows the experimental setup for Example 6;

FIG. 9 shows the results of a one-step hybridisation assay.

The following examples illustrate improved sensitivity of detection oftarget nucleic acid using methods of the invention. The examples relateto detection of a DNA fragment of the cryptic plasmid of Chlamydiatrachomatis (CT).

CT is one of the most common causes of sexually transmitted disease. CTinfections can cause infertility and, during pregnancy, can result inspontaneous abortion, still birth or postpartum endometritis. Inneonates, CT infection can cause blindness and chronic respiratorydisease. Approximately 10% of infected men and upto 70% of infectedwomen do not show symptoms of CT infection. Consequently, accuratediagnosis of CT infection is important so that early treatment of thedisease can be initiated.

In the following examples a dipstick 10 is used to try to detect doublestranded CT target nucleic acid 12 in a sample solution 14. The dipstick10 comprises a strip of nitrocellulose 16 having a contact end 18 forcontacting the sample solution 14 and a capture probe 20 immobilised ata capture zone 22 of the nitrocellulose strip 16 remote from the contactend 18. An anti-biotin antibody-dye conjugate 24 is releasablyimmobilised at a conjugate zone 26 of the nitrocellulose strip locatedbetween the contact end 18 and the capture zone 22. The capture probe 20is capable of hybridising to a first sequence of one strand (the firststrand) of the target nucleic acid 12.

A detection probe 28 and a helper probe 30 each capable of hybridisingto distinct regions of the first strand of the double stranded targetnucleic acid 12 are then added to the sample solution 14. The detectionprobe 28 comprises a nucleic acid coupled to biotin (using methods wellknown to those of skill in the art). The sample solution 14 containingthe detection probe 28 and the helper probe 30 is then heated to atemperature sufficient to separate the complementary strands of thedouble stranded target nucleic acid 12 from each other at least in theregion of the first strand to which the detection probe 28 and helperprobe 30 bind, and then cooled to allow hybridisation of the detectionprobe 28 and the helper probe 30 to the first strand of the doublestranded target nucleic acid. As the detection probe and helper probehybridise to the first strand, the second strand re-anneals to the firststrand, but is prevented from re-annealing to the region of the firststrand which is bound by the detection probe 28 and the helper probe 30.

The contact end 18 of the dipstick 10 is then contacted with the samplesolution 14. The sample solution 14 and any target nucleic acid 12hybridised to the detection probe 28 and the helper probe 30 moves upthe dipstick 10 by capillary action. As the sample solution 14 passesthe conjugate zone 26, it mobilises the anti-biotin antibody-dyeconjugate 24. Released anti-biotin antibody-dye conjugate 24 can thenbind to the biotin coupled to the detection probe 28 hybridised to thetarget nucleic acid 12.

Complex formed between the anti-biotin antibody-dye conjugate 24, thedetection probe 28, the helper probe 30 and the target nucleic acid 12then moves up the dipstick 10 to the capture zone 22 where the targetnucleic acid of the complex can hybridise to the immobilised captureprobe 20. The capture probe 20 is immobilised at the capture zone 22 insuch a way that it cannot be mobilised by the sample solution 14 as itmoves past the capture zone 22. Consequently, the complex bound to thecapture probe remains in the capture zone and can be detected by thepresence of the dye of the anti-biotin antibody-dye conjugate at thecapture zone.

If there is no CT target nucleic acid in the sample solution, thedetection probe 28 cannot be captured at the capture zone 22 and so nodye is visible at the capture zone. If there is CT target nucleic acidin the sample solution, but insufficient amounts of the target nucleicacid can be captured at the capture zone the presence of the targetnucleic acid in the sample solution will not be detected.

The capture of target nucleic acid described above is referred to asdirect probe capture in the examples below. In example 5 below twofurther capture formats were used—universal probe capture and antibodycapture. Universal probe capture relies on capture of the target nucleicacid using a hook probe hybridised to a universal probe immobilised tothe capture zone of the dipstick. The hook probe is capable ofhybridising to the target nucleic acid. The method of capture isidentical to direct probe capture except the capture probe is replacedby the universal and hook probes.

With antibody capture, an antibody is immobilised at the capture zone ofthe dipstick instead of the capture probe. The capture probe comprises aprobe coupled to a ligand (such as DNP) which can be bound by theantibody and is added to the sample solution with the helper anddetection probes. The capture probe hybridises to target nucleic acidwhen the sample solution is heated and then cooled in order to hybridisethe helper and detection probes to the target nucleic acid.

The contact end of the dipstick is contacted with the sample solutionafter incubation of the capture, helper and detection probes in thesample solution. Complex containing the target nucleic acid, captureprobe, helper probe and detection probe (bound by the anti-biotinantibody-dye conjugate) is then captured at the capture zone by theantibody immobilised at the capture zone. Presence of target nucleicacid in the sample solution is again detected by the presence of theanti-biotin antibody-dye conjugate at the capture zone. Thus,hybridisation of the capture probe to the target occurs in the samplesolution rather than on the dipstick.

It has been found that the sensitivity of detection of target nucleicacid can be reduced if the distance between the region of the targetnucleic acid to which the capture probe hybridises and the region towhich the detection probe hybridises is less than 26 nucleotides. Thus,it is preferred that the distance between these regions is at least 26nucleotides and preferably at least 200 nucleotides.

EXAMPLE 1

Experimental Setup

Capture format: direct probe capture (cp) Seq ID No 13 immobilised ondipstick;

Detection format: detection probe (dp) comprising nucleic acid of Seq IDNo 14, 15, 16, or 17 coupled to biotin at 10¹² copies, and ananti-biotin antibody-dye conjugate to detect the detection probe;

Target DNA: 872 bp DNA at 10¹¹-10⁹ copies.

Helper probes: HP SEQ ID No 1′ (24 mer, G+C=9 nucleotides, Tm=72.2° C.,which hybridises to a sequence of the target spaced 11 nucleotides fromthe 5′-end of the capture probe when hybridised to the target nucleicacid) or HP SEQ ID No 1 (24 mer, G+C=8 nucleotides, Tm=70.5° C., whichhybridises to sequence of the target nucleic acid immediately adjacentthe 5′-end of capture probe when hybridised to the target nucleic acid)at 10¹² copies. Results Target copies 10¹¹ 10¹⁰ 5 × 10⁹ 10⁹ Control (nohelper) 2.5 0.0 0.0 0.0 HP SEQ ID No1′ 3.0 1.0 0.0 0.0 HP SEQ ID No1 5.03.5 2.5 0.0

Conclusions

A helper probe improves the sensitivity of target nucleic acid detectionby more than 10-fold.

HP SEQ ID NO:1, which hybridises to a sequence of the target nucleicacid immediately adjacent the 5′-end of the capture probe when this hashybridised to the target nucleic acid, has a stronger helper effect thanHP SEQ ID NO:1, which hybridises to a sequence of the target nucleicacid which is spaced 11 nucleotides from the 5′-end of the capture probewhen this has hybridised to the target nucleic acid. HP SEQ ID NO:1 hasa 2° C. higher Tm than HP SEQ ID NO: 1′. However, the distance betweenthe capture probe and the helper probe is thought to be more importantthan the Tm and G+C content.

EXAMPLE 2

Experimental Setup

Capture format: direct probe capture (cp) (Seq ID No 14) immobilised ondipstick;

Detection format: detection probe (dp) comprising nucleic acid of Seq IDNo 13 coupled to biotin at 10¹² copies, and an anti-biotin antibody-dyeconjugate;

Target DNA: 416 bp DNA at 5×10¹⁰ copies.

Helper probes: combinations of helper probe HP SEQ ID No1, HP SEQ ID No2, HP SEQ ID No 3, Seq ID No 15, Seq ID No 16 and Seq ID No 17 at 10¹²copies.

Results

See FIG. 4

Conclusions

Helper probes which hybridise to a sequence of the target nucleic acidimmediately adjacent the sequence recognized by the capture probe havethe strongest enhancing effect on the sensitivity of detection of targetnucleic acid in this example (compare signal 4.5 with 1.5 for controllacking helper probe).

The effect on the sensitivity of detection of target nucleic acid byhelper probes which hybridise to a sequence of the target nucleic acidimmediately adjacent the sequence recognised by the capture probe ismuch stronger than the effect of helper probes which hybridise tosequences of the target nucleic acid distant from the sequencerecognised by the capture probe (compare signal 4.5 with signal 2.5).

EXAMPLE 3

Experimental Set Up

Capture format: direct probe capture (cp) Seq ID No 14 (immobilised onthe dipstick);

Detection format: detection probe comprising nucleic acid of

Seq ID No 13 (d1), 15 (d3) 16 (d4) or 17 (d5) coupled to biotin at 10¹²copies, and an anti-biotin antibody-dye conjugate;

Target DNA: 872 bp DNA at 10¹⁰ copies.

Helper probes: combinations of helper probes h1=HP SEQ ID No1, h2=HP SEQID No 2, h3=HP SEQ ID No 3, h4=HP SEQ ID No 4, at 10¹² or 10¹³ copies.Results helper at E13 probe at E12 copies copies added 0 h2 + h3 h2 h3h1 + h1 + h2 + h1 + h2 + h2 + h3 h3 + h4 h3 + h4 signal 1.5 3.5 2.5 33.5 3.5 3.5

Conclusions

Helper probes (h2 and h3) which hybridise to sequences of the targetnucleic acid adjacent each side of the sequence recognised by thecapture probe enhance the sensitivity of detection compared to thesensitivity of detection using only one of the helper probes.

Increasing the concentration of helper probe (10¹³ compared to 10¹²copies) did not have any effect on the sensitivity of detection in thisexample.

EXAMPLE 4

Experimental Setup

Capture format: direct probe capture (cp) Seq ID No 14 (immobilised onthe dipstick);

Detection format: detection probe comprising nucleic acid of Seq ID No13 (d1), 15 (d3) 16 (d4) or 17 (d5) coupled to biotin at 10¹² copies,anti-biotin antibody-dye conjugate;

Helper probes: combinations of helper probe h1=HP SEQ ID No1, h2=HP SEQID No 2, h3=HP SEQ ID No 3, h4=HP SEQ ID No 4, at 10¹² or 10¹³ copies;

Targets: circular double stranded DNA plasmids pCTL15B (5.1 Kbp) andpCTL131(6.3 Kbp), plasmid pCTL130 lacking complementary sequences to thecapture and detection probes to act as a negative control, and doublestranded linear DNA (872 bp) at 10¹¹ copies to act as a positivecontrol. Result target h2 + h3 h1 + h2 + h3 + h4 without hp pCTL130 0.00.0 0.0 pCTL131 1.5 1.5 0.0 pCTL15B 1.5 1.5 0.0 872 bp DNA 5.0 5.0 3.5

Conclusion

Circular double stranded DNA, longer than 5 Kbp, could be detected usinghelper probes which hybridise to sequence of the target nucleic adjacentthe sequence recognised by the capture probe.

Helper probes which hybridise to sequence of the target nucleic aciddistant from the sequence recognised by the capture probe but adjacentthe sequence recognised by the detection probe (helper probes h1 and h4)did not enhance the sensitivity of nucleic acid detection in thisexample. Under the conditions in this example the helper probes appearprimarily to enhance hybridisation of the capture probe to the doublestranded circular target nucleic acid on the dipstick.

The sensitivity of detection of the circular double stranded DNA targets(5.1 Kbp or 6.3 Kbp) is lower than the sensitivity of detection of thelinear double stranded 872 bp DNA. As the size of the target nucleicacid increases, the efficiency of hybridisation of the detection andcapture probes to the target nucleic acid is expected to reduce. Theaccessibility of the detection probe to the anti-biotin antibody-dyeconjugate is also thought to be reduced as the target size increases.Detection of double stranded target nucleic acid is thought to be lessefficient than detection of single stranded target nucleic acid becausethe efficiency of hybridisation of the detection probe and the captureprobe to the target nucleic acid decreases. The accessibility of thedetection probe to the anti-biotin antibody-dye conjugate is alsothought to be reduced for double stranded compared to single strandedtarget nucleic acid.

EXAMPLE 5

Experimental Setup

Capture sequence: SEQ ID No 15

Capture formats:

i) direct probe capture—probe Seq ID No 15 immobilised on the dipstick;

ii) universal probe capture—20 nucleotide universal probe immobilised onthe dipstick hybridised to a hook probe with sequence complimentary tothe sequence of the universal probe and to the target DNA sequence (SEQID No 15);

iii) antibody capture—anti-DNP antibody immobilised on the dipstick,capture probe comprising nucleic acid of SEQ ID No 15 coupled to DNP andhybridised to the target nucleic acid in the sample solution;

Detection format: detection probe comprising nucleic acid of Seq ID No13, 14, 16 or 17 coupled to biotin at 10¹² copies, anti-biotinantibody-dye conjugate;

Helper probes: HP SEQ ID No 3 and HP SEQ ID No 4, at 10¹² copies;

Target: 872 bp DNA at 10¹¹ to 10⁸ copies.

Results

See FIG. 7;

Conclusion

The helper probes improved the sensitivity of detection of targetnucleic acid using direct probe capture (see (i) above) and universalprobe capture (see (ii) above). These results support the conclusions ofexamples 2, 3 and 4 that helper probes enhance hybridisation betweennucleic acids on the dipstick.

EXAMPLE 6

Experimental Setup

Capture format: Direct probe capture (cp) (SEQ ID No 10) immobilised onthe dipstick;

Detection format: detection probe (dp) comprising nucleic acid of Seq IDNo 13 coupled to biotin at 10¹² copies, anti-biotin antibody-dyeconjugate;

Helper probes: HP SEQ ID No 5 and HP SEQ ID No 6 which hybridise to asequence of the target nucleic acid adjacent the sequence recognised bySEQ ID No 10; HP SEQ ID No 1 and HP SEQ ID No 2 which hybridise tosequence of the target nucleic acid adjacent the sequence recognised bySEQ ID No 13 at 10¹² copies;

Target: 872 bp DNA at 5×10¹⁰ copies.

Results

See FIG. 8.

Conclusion

When the capture probe and detection probe hybridise to sequences of thetarget nucleic acid which are more than 200 nt apart, the sensitivity ofdetection of target nucleic acid was improved with helper probes thathybridise to sequence of the target nucleic acid adjacent each side ofthe sequence recognised by the detection probe.

EXAMPLE 7

Effect of Helper Probes on CT Detection

Experimental Setup

Capture sequence: SEQ ID No 15

Capture formats:

Direct probe capture: probe comprising nucleic acid of Seq ID No 15coupled to BSA immobilised to the dipstick membrane;

Antibody capture: Anti-DNP antibody (α-DNP capture) immobilised to thedipstick membrane; capture probe comprising nucleic acid of SEQ ID No 15coupled to DNP.

Detection format: detection probe comprising nucleic acid of Seq ID No18 or 13 each coupled to several biotin detection ligands, and ananti-biotin antibody—dye conjugate. 10¹² copies of the detection probes;

Helper probes: HP SEQ ID No 3 and HP SEQ ID No 4, at 10¹² copies. Thehelper probes are capable of hybridising adjacent the region of thetarget nucleic acid recognised by the capture probe;

Target: CT Elementary Bodies's at 2.4 10⁷ copies/test. Results Capture:Direct Probe Capture Ab Capture Helpers Yes No Yes No Signal 4.0 2.5 1.50.5

Conclusions from Example 7

Detection of the cryptic plasmid of CT cells using direct probe captureor antibody capture was improved by the use of helper probes.

Use of helper probes in accordance with the invention 3.0 appears toenhance hybridisation occurring on the dipstick membrane or in solution.

In examples 1 to 7 above, the helper probes hybridise to the same strandof the double stranded target nucleic acid as the capture and detectionprobes. No enhancement of the sensitivity of detection of target nucleicacid was observed in similar experiments in which the helper probeshybridised to the opposite strand of the double stranded target nucleicacid to the strand recognised by the capture and detection probes.

EXAMPLE 8

One-Step Nucleic Acid Dipstick Assay Detection of Chlamydia trachomatis

Experimental Set-Up:

Reagents:

Capture format: oligonucleotide probe capture immobilised on dipstickmembrane via BSA carrier;

Detection format: multiple biotin labelled detector probe; anti-biotinantibody—colloidal gold conjugate;

Sample preparation: Chlamydia trachomatis (Ct) elementary bodies (EB)celles were prepared in ceoncentrations from 10⁶ copies/μl to 10³copies/μl in PBS buffer and heated at 100° C. for 20 minutes;

Hybridisation/dipstick running buffer: Standard is hybridisation buffercomprising salt, detergent and a blocking protein such as BSA orpowdered milk.

Method:

The detection probe, helper probe and 5×10⁶-5×10³ copies of EB dilutedin hybridisation buffer made up to 80 μl and heated at 100° C. for 7minutes. The mixture was then centrifuged briefly to collect all theliquid and mixed with 20 μl anti-biotin Ab colloidal gold. The whole 100μl mixture were wicked up on dipstick and let to develop a signal.

Results and Discussion

The results presented in the Table below and FIG. 9 (see the attachedpower point document) show that about 10⁴ copies of Ct EB could bedetected with one step nucleic acid dipstick assay in less than an hourincluding the sample preparation step.

Although the so presented dipstick detection assay has a sensitivity ofdetection about equal to other sandwich hybridisation assays it has themajor advantages of speed and simplicity.

A sandwich hybridisaiton assay for detection of Ct disclosed in PCT WO93/1322 for example, is a complex multi-component microtitre plateformat assay, which could not be accomplished for less than 5 hours.This assay is a multi-step assay, which requires a gradual addition ofits components in a defined order with incubations and washing stepsafter the addition of every new component.

The nucleic acid dipstick assay subject of this invention could be donein one step with no need of different steps for addition of componentsand washings. This sandwich hybridisation assay does not require morethan one solution conditions in order to render them advantageous forhybridisation and other affinity pair formations. The same solutionconditions could serve a free migration of the components through thedipstick membrane as well.

Methods of the invention have been found to significantly enhance thesensitivity of detection of target nucleic acids by dipsticks. Inparticular, detection of double stranded nucleic acid and circulardouble stranded target nucleic acid is greatly improved. B) Direct ProbeC) Universal Probe A) Ab Capture Capture Capture Signal 5×E9 3.5 2.0 3.0Sensitivity E9 5×E9 E9 D) Ab Capture- E) Direct Probe F) Universal Probewith helper probes Capture-with Capture-with helper probes helper probesSignal 5×E9 3.5 4.0 3.0 Sensitivity E9 5×E8 5×E8 (very faint) Figurelegends

One-step nucleic acid dipstick assay detection of Chlamydia trachomatisThe numbers indicate the number of elementary bodies of Chlamydiatrachomatis *NC: Negative control Table: One-step nucleic acid dipstickassay detection of Chlamydia trachomatis

1. A method for testing for the presence of a target nucleic acid in asample solution comprising: a) providing a chromatographic strip havinga contact end for contacting the sample solution, and a capture probethat is immobilized at a capture zone of the chromatographic stripremote from the contact end, wherein the capture probe is capable ofhybridizing to a first sequence of the target nucleic acid; b)incubating the sample solution with: a detection probe capable ofattaching to the target nucleic acid under conditions for attachment ofthe detection probe to target nucleic acid, thereby allowing direct orindirect detection of target nucleic acid utilizing the detection probe,and a first helper probe capable of hybridizing to a second sequence ofthe target nucleic acid and thereby enhancing hybridization of thecapture probe to target nucleic acid, wherein the sample solution andthe first helper probe are incubated under conditions for hybridizationof the first helper probe to the second sequence; c) contacting thecontact end of the chromatographic strip with the sample solution sothat a complex formed between the detection probe, the first helperprobe and target nucleic acid can move by capillary action to thecapture zone and bind to the capture zone by hybridization of thecapture probe to the target nucleic acid of the complex; and d) checkingfor the presence of the detection probe at the capture zone.
 2. A methodfor testing for the presence of a target nucleic acid in a samplesolution comprising: a) providing a chromatographic strip having acontact end for contacting the sample solution, and a capture moietyimmobilized at a capture zone of the chromatographic strip remote fromthe contact end; b) incubating the sample solution with: a detectionprobe capable of attaching to the target nucleic acid under conditionsfor attachment of the detection probe to target nucleic acid, therebyallowing direct or indirect detection of target nucleic acid utilizingthe detection probe, a capture probe capable of hybridizing to a firstsequence of the target nucleic acid under conditions for hybridizationof the capture probe to the first sequence, wherein the capture probe iscapable of binding the capture moiety when the capture probe ishybridized to the first sequence, and a first helper probe capable ofhybridizing to a second sequence of the target nucleic acid and therebyenhancing hybridization of the capture probe to target nucleic acid,wherein the sample solution and the first helper probe are incubatedunder conditions for hybridization of the first helper probe to thesecond sequence; c) contacting the contact end of the chromatographicstrip with the sample solution so that a complex formed between thedetection probe, the capture probe, the first helper probe and targetnucleic acid can move by capillary action to the capture zone and bindto the capture zone by binding of the capture moiety to the captureprobe of the complex; and d) checking for the presence of the detectionprobe at the capture zone.
 3. The method according to claim 1, whereinthe second sequence is spaced up to 10 nucleotides from the firstsequence.
 4. The method according to claim 3, wherein the secondsequence is immediately adjacent to the first sequence.
 5. The methodaccording to claim 1, wherein the sample solution is incubated with asecond helper probe capable of hybridizing to a third sequence of thetarget nucleic acid and thereby enhancing hybridization of the captureprobe to target nucleic acid, wherein the sample solution and the secondhelper probe are incubated under conditions for hybridization of thesecond helper probe to the third sequence.
 6. The method according toclaim 5, wherein the second and third sequences flank the firstsequence.
 7. The method according to claim 6, wherein the third sequenceis spaced up to 10 nucleotides from the first sequence.
 8. The methodaccording to claim 7, wherein the third sequence is immediately adjacentto the first sequence.
 9. The method according to claim 1, wherein thedetection probe comprises a hook detection probe capable of hybridizingto the target nucleic acid; and a universal detection probe capable ofhybridizing to the hook detection probe.
 10. The method according toclaim 1, wherein the detection probe is capable of hybridizing to afourth sequence of the target nucleic acid to attach the detection probeto the target nucleic acid.
 11. The method according to claim 10,wherein the sample solution is incubated with a third helper probecapable of hybridizing to a fifth sequence of the target nucleic acid,thereby enhancing hybridization of the detection probe to the fourthsequence, wherein the third helper probe and the sample solution areincubated under conditions for hybridization of the third helper probeto the fifth sequence.
 12. A method for testing for the presence of atarget nucleic acid in a sample solution comprising: a) providing achromatographic strip having a contact end is for contacting the samplesolution, and a capture probe immobilized at a capture zone of thechromatographic strip remote from the contact end, wherein the captureprobe is capable of hybridizing to the target nucleic acid; b)contacting the sample solution with a helper probe capable ofhybridizing to the target nucleic acid and thereby enhancinghybridization of the capture probe to the target nucleic acid, whereinthe sample solution is contacted with the helper probe under conditionsfor hybridization of the helper probe to the target nucleic acid; c)contacting the contact end of the chromatographic strip with the samplesolution to cause sample solution to move by capillary action to thecapture zone so that a complex formed between the helper probe and thetarget nucleic acid can be captured at the capture zone by hybridizationof the capture probe to the target nucleic acid of the complex; and d)checking for the presence of the target nucleic acid at the capturezone.
 13. A method for testing for the presence of a target nucleic acidin a sample solution comprising: a) providing a chromatographic striphaving a contact end for contacting the sample solution, and a capturemoiety immobilized at a capture zone of the chromatographic strip remotefrom the contact end; b) contacting the sample solution with: a captureprobe capable of hybridizing to the target nucleic acid under conditionsfor hybridization of the capture probe to the target nucleic acid,wherein the capture probe is capable of binding the capture moiety whenthe capture probe is hybridized to the target nucleic acid, and a helperprobe capable of hybridizing to the target nucleic acid and therebyenhancing hybridization of the capture probe to the target nucleic acid,wherein the sample solution and the helper probe is contacted underconditions for hybridization of the helper probe to the target nucleicacid; c) contacting the contact end of the chromatographic strip withthe sample solution to cause sample solution to move by capillary actionto the capture zone so that a complex formed between the capture probe,the helper probe, and the target nucleic acid can be captured at thecapture zone by binding of the capture moiety to the capture probe ofthe complex; and d) checking for the presence of target nucleic acid atthe capture zone.
 14. The method according to claim 12, wherein thecapture probe comprises a universal capture probe hybridized to a hookcapture.
 15. A method for testing for the presence of a target nucleicacid in a sample solution comprising: a) providing a chromatographicstrip having a contact end for contacting the sample solution, and acapture probe immobilized at a capture zone of the chromatographic stripremote from the contact end, wherein the capture probe is capable ofhybridizing to a first sequence of the target nucleic acid; b)incubating the sample solution with: a detection probe capable ofhybridizing to a second sequence of the target nucleic acid underconditions for hybridization of the detection probe to target nucleicacid, thereby allowing direct or indirect detection of the targetnucleic acid utilizing the detection probe, and a first helper probecapable of hybridizing to a third sequence of the target nucleic acidand thereby enhancing hybridization of the detection probe to the secondsequence, wherein the sample solution and the first helper probe areincubated under conditions for hybridization of the first helper probeto the third sequence; c) contacting the contact end of thechromatographic strip with the sample solution so that a complex formedbetween the detection probe, the first helper probe, and the targetnucleic acid can move by capillary action to the capture zone and bindto the capture zone by hybridization of the capture probe to the targetnucleic acid of the complex; and. d) checking for the presence of thedetection probe at the capture zone.
 16. A method for testing for thepresence of a target nucleic acid in a sample solution comprising: a)providing a chromatographic strip having a contact end for contactingthe sample solution, and a capture moiety immobilized at a capture zoneof the chromatographic strip remote from the contact end; b) incubatingthe sample solution with: a capture probe capable of hybridizing to afirst sequence of the target nucleic acid under conditions forhybridization of the capture probe to the first sequence, wherein thecapture probe is capable of binding the capture moiety when the captureprobe is hybridized to the first sequence, a detection probe capable ofhybridizing to a second sequence of the target nucleic acid underconditions for hybridization of the detection probe to the secondsequence, thereby allowing direct or indirect detection of targetnucleic acid utilizing the detection probe, and a first helper probecapable of hybridizing to a third sequence of the target nucleic acidand thereby enhancing hybridization of the detection probe to targetnucleic acid, wherein the sample solution and the first helper probe areincubated under conditions for hybridization of the first helper probeto the third sequence; c) contacting the contact end of thechromatographic strip with the sample solution so that a complex formedbetween the detection probe, the capture probe, the first helper probe,and the target nucleic acid can move by capillary action to the capturezone and bind to the capture zone by binding of the capture moiety tothe capture probe of the complex; and d) checking for the presence ofdetection probe at the capture zone.
 17. The method according to claim15, wherein the third sequence is spaced up to 10 nucleotides from thesecond sequence.
 18. The method according to claim 17, wherein the thirdsequence is immediately adjacent to the second sequence.
 19. The methodaccording to claim 15, wherein the sample solution is incubated with asecond helper probe capable of hybridizing to a fourth sequence of thetarget nucleic acid and thereby enhancing hybridization of the detectionprobe to target nucleic acid, wherein the sample solution and the secondhelper probe are incubated under conditions for hybridization of thesecond helper probe to the fourth sequence.
 20. The method according toclaim 19, wherein the third and as fourth sequences flank the secondsequence.
 21. The method according to claim 20, wherein the fourthsequence is spaced up to 10 nucleotides from the second sequence. 22.The method according to claim 21, wherein the fourth sequence isimmediately adjacent to the second sequence.
 23. The method according toclaim 15, wherein the capture probe comprises a universal capture probehybridized to a hook capture probe.
 24. The method according to claim15, wherein hybridization of the probes to target nucleic acid in thesample solution is carried out in a single step.
 25. A method fortesting for the presence of a target nucleic acid in a sample solutioncomprising: a) providing a chromatographic strip having a contact endfor contacting the sample solution, a capture probes immobilized at acapture zone of the chromatographic strip remote from the contact end,wherein the capture probe is capable of hybridizing to the targetnucleic acid, and a helper probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the helper probe is capable of hybridizing to the target nucleicacid and thereby enhancing hybridization of the capture probe to thetarget nucleic acid; b) contacting the contact end of thechromatographic strip with the sample solution to cause sample solutionto move by capillary action to the capture zone, thereby releasinghelper probe from the chromatographic strip and allowing released helperprobe to hybridize to target nucleic acid in the sample solution as ittravels to the capture zone, so that a complex comprising target nucleicacid and helper probe can be captured at the capture zone byhybridization of the capture probe to the target nucleic acid of thecomplex; and c) checking for the presence of the target nucleic acid atthe capture zone.
 26. A method for testing for the presence of a targetnucleic acid in a sample solution comprising: a) providing achromatographic strip having a contact end for contacting the samplesolution, a capture moiety immobilized at a capture zone of thechromatographic strip remote from the contact end, and a capture probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the capture probe is capable ofhybridizing to the target nucleic acid and capable of binding thecapture moiety when the capture probe is hybridized to the targetnucleic acid; b) incubating the sample solution with: a helper probecapable of hybridizing to the target nucleic acid and thereby enhancinghybridization of the capture probe to target nucleic acid, underconditions for hybridization of the helper probe to the target nucleicacid; and c) contacting the contact end of the chromatographic stripwith the sample solution to cause sample solution to move by capillaryaction to the capture zone, thereby releasing capture probe from thechromatographic strip so that released capture probe can hybridize totarget nucleic acid in the sample solution as it travels to the capturezone, and so that a complex comprising target nucleic acid, captureprobe and helper probe can be captured at the capture zone by binding ofthe capture moiety to the capture probe of the complex; and d) checkingfor the presence of target nucleic acid at the capture zone.
 27. Amethod for testing for the presence of a target nucleic acid in a samplesolution comprising: a) providing a chromatographic strip having acontact end for contacting the sample solution, a capture moietyimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, a capture probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the capture probe is capable of hybridizing to the targetnucleic acid and capable of binding the capture moiety when the captureprobe is hybridized to the target nucleic acid, and a helper probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the helper probe is capable ofhybridizing to the target nucleic acid and thereby enhancinghybridization of the capture probe to the target nucleic acid; and b)contacting the contact end of the chromatographic strip with the samplesolution to cause sample solution to move by capillary action to thecapture zone, thereby releasing the capture probe and the helper probefrom the chromatographic strip so that released the capture probe andthe helper probe can hybridize to the target nucleic acid in the samplesolution as it travels to the capture zone, and so that a complexcomprising the target nucleic acid, the capture probe and the helperprobe can be captured at the capture zone by binding of the capturemoiety to the capture probe of the complex; and d) checking for thepresence of the target nucleic acid at the capture zone.
 28. A methodfor testing for the presence of a target nucleic acid in a samplesolution comprising: a) providing a chromatographic strip having acontact end for contacting the sample solution, a capture probeimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, wherein the capture probe is capable of hybridizing tothe target nucleic acid, and a detection probe releasably immobilized tothe chromatographic strip between the contact end and the capture zone,wherein the detection probe is capable of hybridizing to the targetnucleic acid and thereby allowing direct or indirect detection of thetarget nucleic acid utilizing the detection probe; b) incubating thesample solution with: a helper probe capable of hybridizing to thetarget nucleic acid and thereby enhancing hybridization of the detectionprobe to the target nucleic acid, wherein the sample solution and thehelper probe are incubated under conditions for hybridization of thehelper probe to the target nucleic acid; c) contacting the contact endof the chromatographic strip with the sample solution to cause thesample solution to move by capillary action to the capture zone, therebyreleasing the detection probe from the chromatographic strip so thatreleased the detection probe can hybridize to the target nucleic acid inthe sample solution as it travels to the capture zone, and so that acomplex comprising the target nucleic acid, the helper probe, and thedetection probe can be captured at the capture zone by hybridization ofthe capture probe to the target nucleic acid of the complex; and d)checking for the presence of the detection probe at the capture zone.29. A method for testing for the presence of a target nucleic acid in asample solution comprising: a) providing a chromatographic strip havinga contact end for contacting the sample solution, a capture probeimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, wherein the capture probe is capable of hybridizing tothe target nucleic acid, a detection probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the detection probe is capable of hybridizing to the targetnucleic acid and thereby allowing direct or indirect detection of targetnucleic acid utilizing the detection probe, and a helper probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the helper probe is capable ofhybridizing to the target nucleic acid and thereby enhancinghybridization of the detection probe to the target nucleic acid; and b)contacting the contact end of the chromatographic strip with the samplesolution to cause sample solution to move by capillary action to thecapture zone, thereby releasing the helper probe and the detection probefrom the chromatographic strip so that released the helper probe and thedetection probe can hybridize to target nucleic acid in the samplesolution as it travels to the capture zone, and so that a complexcomprising the target nucleic acid, the helper probe, and the detectionprobe can be captured at the capture zone by hybridization of thecapture probe to the target nucleic acid of the complex; and d) checkingfor the presence of the detection probe at the capture zone.
 30. Amethod for testing for the presence of a target nucleic acid in a samplesolution comprising: a) providing a chromatographic strip having: acontact end for contacting the sample solution, a capture moietyimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, and a capture probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the capture probe is capable of hybridizing to the targetnucleic acid and is capable of binding the capture moiety when thecapture probe is hybridized to the target nucleic acid; b) incubatingthe sample solution with: a detection probe capable of hybridizing tothe target nucleic acid thereby allowing direct or indirect detection oftarget nucleic acid utilizing the detection probe, wherein the detectionprobe is incubated with the sample solution under conditions forhybridization of the detection probe to the target nucleic acid, and ahelper probe capable of hybridizing to the target nucleic acid andthereby enhancing hybridization of the detection probe to the targetnucleic acid, wherein the sample solution and the helper probe areincubated under conditions for hybridization of the helper probe to thetarget nucleic acid; c) contacting the contact end of thechromatographic strip with the sample solution to cause sample solutionto move by capillary action to the capture zone thereby releasing thecapture probe from the chromatographic strip so that the releasedcapture probe can hybridize to the target nucleic acid in the samplesolution as it travels to the capture zone, and so that a complexcomprising the target nucleic acid, the capture probe, the helper probe,and the detection probe can be captured at the capture zone by bindingof the capture moiety to the capture probe of the complex; and d)checking for the presence of the detection probe at the capture zone.31. A method for testing for the presence of a target nucleic acid in asample solution comprising: a) providing a chromatographic strip havinga contact end for contacting the sample solution, a capture moietyimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, and a detection probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the detection probe is capable of hybridizing to the targetnucleic acid thereby allowing direct or indirect detection of the targetnucleic acid utilizing the detection probe; b) incubating the samplesolution with: a capture probe capable of hybridizing to the targetnucleic acid and capable of binding the capture moiety when the captureprobe is hybridized to the target nucleic acid, under conditions forhybridization of the capture probe to the target nucleic acid, and ahelper probe capable of hybridizing to the target nucleic acid andthereby enhancing hybridization of the detection probe to the targetnucleic acid, under conditions for hybridization of the helper probe tothe target nucleic acid; c) contacting the contact end of thechromatographic strip with the sample solution to cause sample solutionto move by capillary action to the capture zone, thereby releasing thedetection probe from the chromatographic strip so that the releaseddetection probe can hybridize to the target nucleic acid in the samplesolution as it travels to the capture zone, and so that a complexcomprising the target nucleic acid, the capture probe, the helper probe,and the detection probe can be captured at the capture zone by bindingof the capture moiety to the capture probe of the complex; and d)checking for the presence of the detection probe at the capture zone.32. A method for testing for the presence of a target nucleic acid in asample solution comprising: a) providing a chromatographic strip havinga contact end for contacting the sample solution, a capture moietyimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, a detection probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the detection probe is capable of hybridizing to the targetnucleic acid thereby allowing direct or indirect detection of targetnucleic acid utilizing the detection probe, and a helper probereleasably immobilized to the chromatographic strip, wherein the helperprobe is capable of hybridizing to the target nucleic acid and therebyenhancing hybridization of the detection probe to the target nucleicacid; b) incubating the sample solution with: a capture probe capable ofhybridizing to the target nucleic acid and capable of binding thecapture moiety when the capture probe is hybridized to the targetnucleic acid, wherein the capture probe is incubated with the samplesolution under conditions for hybridization of the capture probe to thetarget nucleic acid, and a helper probe capable of hybridizing to thetarget nucleic acid and thereby enhancing hybridization of the detectionis probe to the target nucleic acid, wherein the helper probe isincubated with the sample solution under conditions for hybridization ofthe helper probe to the target nucleic acid; c) contacting the contactend of the chromatographic strip with the sample solution to cause thesample solution to move by capillary action to the capture zone, therebyreleasing the detection probe and the helper probe from thechromatographic strip so that the released detection probe and thehelper probe can hybridize to the target nucleic acid in the samplesolution as it travels to the capture zone, and so that a complexcomprising the target nucleic acid, the capture probe, the helper probe,and the detection probe can be captured at the capture zone by bindingof the capture moiety to the capture probe of the complex; and d)checking for the presence of the detection probe at the capture zone.33. A method for testing for the presence of a target nucleic acid in asample solution comprising: a) providing a chromatographic strip havinga contact end for contacting the sample solution, a capture moietyimmobilized at a capture zone of the chromatographic strip remote fromthe contact end, a detection probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the detection probe is capable of hybridizing to the targetnucleic acid thereby allowing direct or indirect detection of targetnucleic acid utilizing the detection probe, and a capture probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the capture probe is capable ofhybridizing to the target nucleic acid and capable of binding thecapture moiety when the capture probe is hybridized to the targetnucleic acid; b) incubating the sample solution with a helper probecapable of hybridizing to the target nucleic acid and thereby enhancinghybridization of the detection probe to target nucleic acid, wherein thehelper probe is incubated with the sample solution under conditions forhybridization of the helper probe to the target nucleic acid; c)contacting the contact end of the chromatographic strip with the samplesolution to cause the sample solution to move by capillary action to thecapture zone, thereby releasing the detection probe and the captureprobe from the chromatographic strip so that the released detectionprobe and the released capture probe can hybridize to target nucleicacid in the sample solution as lit travels to the capture zone, and sothat a complex comprising the target nucleic acid, the capture probe,the helper probe and the detection probe can be captured at the capturezone by binding of the capture moiety to the capture probe of thecomplex; and d) checking for the presence of the detection probe at thecapture zone.
 34. A method for testing for the presence of a targetnucleic acid in a sample solution comprising: a) providing achromatographic strip having a contact end for contacting the samplesolution, a capture moiety immobilized at a capture zone of thechromatographic strip remote from the contact end, a detection probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the detection probe is capable ofhybridizing to the target nucleic acid thereby allowing direct orindirect detection of target nucleic acid utilizing the detection probe,a helper probe releasably immobilized to the chromatographic stripbetween the contact is end and the capture zone, wherein the helperprobe is capable of hybridizing to the target nucleic acid and therebyenhancing hybridization of the detection probe to the target nucleicacid, and a capture probe releasably immobilized to the chromatographicstrip between the contact end and the capture zone, wherein the captureprobe is capable of hybridizing to the target nucleic acid and capableof binding the capture moiety when the capture probe is hybridized tothe target nucleic acid; b) contacting the contact end of thechromatographic strip with the sample solution to cause the samplesolution to move by capillary action to the capture zone, therebyreleasing the detection probe, the helper probe and the capture probefrom the chromatographic strip so that the released detection probe, thehelper probe and the capture probe can hybridize to the target nucleicacid in the sample solution as it travels to the capture zone, and sothat a complex comprising the target nucleic acid, the capture probe,the helper probe, and the detection probe can be captured at the capturezone by binding of the capture moiety to the capture probe of thecomplex; and c) checking for the presence of the detection probe at thecapture zone.
 35. A kit for testing for the presence of a target nucleicacid in a sample solution suspected of containing the target nucleicacid, wherein the kit comprises: i) a dipstick comprising: achromatographic strip having a contact end for contacting the samplesolution; and a capture probe that is immobilized at a capture zone ofthe chromatographic strip remote from the contact end, wherein thecapture probe is capable of hybridizing to a first sequence of thetarget nucleic acid; and ii) a helper probe capable of hybridizing to asecond sequence of the target nucleic acid and thereby enhancinghybridization of the capture probe to the target nucleic acid.
 36. Thekit according to claim 35, wherein the helper probe is releasablyimmobilized to the chromatographic strip between the contact end and thecapture zone.
 37. A kit for testing for the presence of a target nucleicacid in a sample solution suspected of containing the target nucleicacid, wherein the kit comprises: i) a dipstick comprising: achromatographic strip having a contact end for contacting the samplesolution and a capture probe that is immobilized at a capture zone ofthe chromatographic strip remote from the contact end, wherein thecapture probe is capable of hybridizing to a first sequence of thetarget nucleic acid; ii) a detection probe capable of hybridizing to asecond sequence of the target nucleic acid to allow direct or indirectdetection of the target nucleic acid; and iii) a helper probe capable ofhybridizing to a third sequence of the target nucleic acid and therebyenhancing hybridization of the detection probe to the second sequence.38. The kit according to claim 37, wherein the detection probe isreleasably immobilized to the chromatographic strip between the contactend and the capture zone.
 39. The kit according to claim 37, wherein thedetection probe and the helper probe are releasably immobilized to thechromatographic strip between the contact end and the capture zone. 40.A kit for testing for the presence of a target nucleic acid in a samplesolution suspected of containing the target nucleic acid, wherein thekit comprises: i) a dipstick comprising: a chromatographic strip havinga contact end for contacting the sample solution and a capture moietythat is immobilized at a capture zone of the chromatographic stripremote from the contact end; ii) a capture probe capable of hybridizingto a first sequence of the target nucleic acid, which can be bound bythe capture moiety when the capture probe is hybridized to the firstsequence; and iii) a helper probe capable of hybridizing to a secondsequence of the target nucleic acid and thereby enhancing hybridizationof the capture probe to the first sequence.
 41. The kit according toclaim 40, wherein the capture probe is releasably immobilized to thechromatographic strip between the contact end and the capture zone. 42.The kit according to claim 40, wherein the capture probe and the helperprobe are releasably immobilized to the chromatographic strip betweenthe contact end and the capture zone.
 43. A kit for testing for thepresence of a target nucleic acid in a sample solution suspected ofcontaining the target nucleic acid, wherein the kit comprises: i) adipstick comprising: a chromatographic strip having a contact end forcontacting the sample solution and a capture moiety that is immobilizedat a capture zone of the chromatographic strip remote from the contactend; ii) a capture probe capable of hybridizing to a first sequence ofthe target nucleic acid, which can be bound by the capture moiety whenthe capture probe is hybridized to the first sequence; iii) a detectionprobe capable of hybridizing to a second sequence of the target nucleicacid to allow direct or indirect detection of the target nucleic acid;and iv) a helper probe capable of hybridizing to a third sequence of thetarget nucleic acid and thereby enhancing hybridization of the detectionprobe to the second sequence.
 44. The kit according to claim 43, whereinthe capture probe and the detection probe is releasably immobilized tothe chromatographic strip between the contact end and the capture zone.45. The kit according to claim 43, wherein the helper probe and thedetection probe are releasably immobilized to the chromatographic stripbetween the contact end and the capture zone.
 46. A chromatographicstrip for testing for the presence of a target nucleic acid in a samplesolution, wherein the chromatographic strip comprises: a contact end forcontacting the sample solution; a capture is probe that is immobilizedat a capture zone of the chromatographic strip remote from the contactend, wherein the capture probe is capable of hybridizing to the targetnucleic acid; and a helper probe releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the helper probe is capable of hybridizing to the target nucleicacid and thereby enhancing hybridization of the capture probe to thetarget nucleic acid.
 47. A chromatographic strip for testing for thepresence of a target nucleic acid in a sample solution, wherein thechromatographic strip comprises: a contact end for contacting the samplesolution; a capture probe that is immobilized at a capture zone of thechromatographic strip remote from the contact end, wherein the captureprobe is capable of hybridizing to the target nucleic acid; and a helperprobe releasably immobilized to the chromatographic strip between thecontact end and the capture zone, wherein the helper probe is capable ofhybridizing to the target nucleic acid and thereby enhancinghybridization of a detection probe to the target nucleic acid.
 48. Achromatographic strip for testing for the presence of a target nucleicacid in a sample solution, wherein the chromatographic strip comprises:a contact end for contacting the sample solution; a capture moiety thatis immobilized at a capture zone of the chromatographic strip remotefrom the contact end, wherein the capture moiety is capable of binding acapture probe hybridized to the target nucleic acid; a capture probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the capture probe is capable ofhybridizing to the target nucleic acid and thereby enhancinghybridization of the capture probe to the target nucleic acid.
 49. Achromatographic strip for testing for the presence of a target nucleicacid in a sample solution, wherein the chromatographic strip comprises:a contact end for contacting the sample solution; a capture moiety thatis immobilized at a capture zone of the chromatographic strip remotefrom the contact end, wherein the capture moiety is capable of binding acapture probe hybridized to the target nucleic acid; a detection probereleasably immobilized to the chromatographic strip between the contactend and the capture zone, wherein the detection probe is capable ofhybridizing to the target nucleic acid thereby allowing direct orindirect detection of target nucleic acid utilizing the detection probe.50. A dipstick assay to test for the presence of a target nucleic acidin a sample solution, wherein the dipstick comprises a helper probe. 51.The dipstick assay according to claim 50, wherein the helper probeenhances hybridization of a capture probe or a detection is probe to thetarget nucleic acid.
 52. An isolated nucleic acid molecule or nucleicacid analogue, wherein the nucleic acid comprises a polynucleotidesequence selected from the group consisting of SEQ ID NOS: 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, and
 18. 53. A method fortesting the presence of CT target nucleic acid in a sample solutioncomprising a helper probe to enhance the detection of CT target nucleicacid, wherein the helper probe comprises the polynucleotide of claim 52.55. A method of testing the presence of a target nucleic acid in asample solution comprising the kit of claim
 35. 56. A method of testingthe presence of a target nucleic acid in a sample solution comprisingthe chromatographic strip of claim
 49. 57. The kit of claim 35 furthercomprising a detection probe capable of attaching to the target nucleicacid to allow direct or indirect detection of the target nucleic acid.58. The kit of claim 40 further comprising a detection probe capable ofattaching to the target nucleic acid to allow direct or indirectdetection of the target nucleic acid.
 59. The kit according to claim 43,wherein the helper probe, the detection probe, and the capture probe arereleasably immobilized to the chromatographic strip between the contactend and the capture zone.
 60. The chromatographic strip of claim 48further comprising a helper probe that is releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the helper probe is capable of hybridizing the target nucleicacid, thereby enhancing hybridization of the capture probe to the targetnucleic acid.
 61. The chromatographic strip of claim 49 furthercomprising: i) a capture probe that is releasably immobilized to thechromatographic strip between the contact end and the capture zone,wherein the capture probe is capable of hybridizing to the targetnucleic acid and capable of binding the capture moiety; and ii) a helperprobe that is capable of hybridizing to the target nucleic acid, therebyenhancing hybridization of the detection probe to the target nucleicacid.